Problems trying to install Win7Pro on a Dell bought with Win10

Hi,
I bought my Dell Inspiron 10 7000 (7559) in Feb, it has been nothing but trouble, which I am sure relates to Win10, so I want to downgrade.
(My understanding was that it was an original Win10 machine, but since attempting this Win7 install I have realised that it may not be the case.)
I have a Win7Pro key and had a friend make a bootable USB as the Dell has no disc drive.
I did a lot of combing various sites for info on how to do this with a Dell, and even then I was still unsure how to proceed because of the safe boot and UEFI function. So I contacted Dell; the technician went through his manual on how to deal with the UEFI safe mode boot, legacy changes in the BIOS, it all looked good, I thought it would work. But it didn't -- we tried several times with the Dell technician on the phone.
Here is what happened:
On start up with 'boot from USB' selected in the BIOS it would load a Win7 splash screen (note: not Win7Pro) but the USB didn't flash and come to life; it would open a Win7 window asking me to select timezone, region and keyboard, I made my selection and clicked install, then it asked me where to install Win7 from, the options were:
C drive 'OS' (please note the original drive has not been wiped so Win10 and Dell partitions are still as they were)
X Drive 'Boot'.
No matter which I selected the response was the same: 'files not found'.

I am stuck, have no idea how to proceed; should I have wiped the laptop hard drive to start with -- even though the Dell tech didn't think it was necessary?
Or, is it possible that the computer was simply upgraded to Win10 from Win7 (not pro) before I bought it and the reason I get the Win7 screen, and subsequent question where to download from, is that the original install supercedes the USB?

Help please.

The easy way to tell the original OS what sticker have you got on it.
The Big w7 or the tiny postage stamp sized one 8 or 10.

Now as for installing W7 theres NO way you can install it properly in SAFE boot mode (X) partition, Its gotta be on another
i suspect your current set-up C = W10 D = system recovery so youll have to put 7 on E,

Also depends if you only want 7, you can upgrade to 10 for free until july.

Roy

Hi Roy,
I mentioned it in the original post, I think, that I *realllly* (lol, can I stress that enough?) do not want win10. I have bought the win7pro key to replace it.

You might have thought there would be a windows sticker with water mark on the bottom of the laptop, but alas no, it is a Dell, I have no idea if that is standard practice or not, but all my Acers have them. It says on the box that it is a Win10 model, but it is on a description tag rather than an authentificiation sticker, that's all I have.

I agree that the C drive probably relates to the Win10 that is already on the laptop, but how is it seeing this on the USB boot drive since the bios is booting from it?

Can I do this whole thing from inside Win10, to make a partition install win7pro and then boot from there?

Thrashzone,
I am in the UK, I did not buy from Dell, and I cannot find Win7 on a worthy laptop here. That's why I bought this, after long deliberation and having been reassured that Win10 would work as a brand new install.
I guess that advice was wrong. But even so, when I first had probs in feb, and called Dell, they said they would replace it, yet for some silly reason I tried to persevere and the offer to replace has now expired. <sigh>

Don't you just hate that!?

Hi,
you can follow this tutorial for a clean install,(W7 only)
In your case i would make a system image to be on the safe side.

Clean Install Windows 7

With regard to your purchase of W7 pro, there are quite a few dodgy sites selling them, if you paid £100+ your in the right ballpark anything less it will likely be counterfiet.

Try inside the battery compartment for the label,

Roy